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First steps for software developers:

Golang for ARM-Linux systems

The Golang gopher

This manual is intended to serve as an introduction to the development of individual communication and automation solutions based on ARM-Linux systems in Go.

This language developed by Google is fast and easy to learn, but in contrast to script languages it is also very powerful and high-performance. It comes with a cross-compiler for ARM-Linux systems and offers a very simple workflow for programming the pure.box, the versatile communication and automation server from Wiesemann & Theis.

After installing and configuring a work environment, this tutorial shows you how to work with the Gotool using the command line with the example of a simple Hello-World program for the pure.box.

Step 1: Install Go

Go is free software and can be downloaded from the project page. Alternately you can install Go from the package sources. After installation a few environment variables must be set and adjusted.

  • PATH
    The environment variable PATH must have the sub-directory bin added in the GO directory so that Go can be run system-wide.
  • GOROOT
    The environment variable GOROOT contains the path to the directory of the Go installation. This variable is only set if Go was installed ion a different directory than the standard directory /usr/local/go.
  • GOPATH
    The environment variable GOPATH contains the path to the working director of the user. This directory will later contain the sub-directories src for sources, lib for pre-compiled libraries, and bin for executable files.

Setting the environment variables

First set the variable GOPATH to your personal working directory. Then process the file .bashrc in your home directory and there insert for example the following line.

					
						export GPOATH=~/go
					
				

If you have not installed Go from the packet sources, you must now set the variable GOROOT and expand the variable PATH. For practical reasons these changes are set for the entire system. Therefore, use root rights to edit the file /etc/profile and insert here both the following lines:

					
						#Pfad zum Installationsverzeichnis von Go
						export GOROOT=/usr/local/go
						export PATH=$PATH:$GOROOT/bin
					
				

Install Git

To install language extensions and packages from third parties without great effort, Go uses Git, the software developed by Linus Torvalds for distributed version management. This can be downloaded from www.git.scm-com

Check installation

The go tool is the Swiss army knife for Go development. To check whether the installation was successful, you can use it now to display the Go environment.

In the terminal enter the following command:

					go env
				

An overview of all environment variables relevant to Go is now output:

					
						GOARCH="amd64"
						GOBIN=""
						GOEXE=""
						GOHOSTARCH="amd64"
						GOHOSTOS="linux"
						GOOS="linux"
						GOPATH="/home/martin/go"
						GORACE=""
						GOROOT="/usr/lib/go"
						GOTOOLDIR="/usr/lib/go/pkg/tool/linux_amd64"
						CC="gcc"
						GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build863343041=/tmp/go-build -gno-record-gcc-switches"
						CXX="g++"
						CGO_ENABLED="1"
					
				

If an error message is displayed, the bin directory in GOROOT is probably not in the search path. Check the environment variable PATH using the command echo %PATH%. Then check whether GOPATH matches your working directory.

Step 2: Hello, World

Go programs are developed within the GOPATH in the directory src. Create here the directory hello and in it the file hello.go.

				
					package main

					import "fmt"

					func main() {
						fmt.Println("Hello, world!")
					}
				
			
  •  If you want to create an executable file in Go, work in the package main.
  •  The package fmt provides functions for in- and output.
  •  The function main() is the entry point to the program.
  •  fmt.PrintIn() outputs a string followed by a newline character.

To compile the program, enter the following command:

				go install github.com/wut/tutorial/hello
			

If you have not received an error message, the translation was successful. The executable file hello.exe can now be found in the bin directory of the Go-Path.

				
					./hello
					Hello World!
				
			

Step 3: Hello pure.box - Cross-compilation for ARM-Linux

Go makes it very simple to compile applications for other target platforms. To translate the Hello World example for the pure.box, you must simply set a few temporary environment variables:

  • GOARCH
    The environment variable GOARCH sets the target architecture. For the pure.box this is arm.
  • GOOS
    This is the operating system of the target platform. For the pure.box this variable must be set to linux.
  • GOARM
    GOARM tells the compiler how it should handle floating point operations. The value for the pure.box is 5.

Enter the following in the entry prompt:

				
					export GOOS=linux
					export GOARCH=arm
					export GOARM=5
				
			

Start the cross-platform translation by changing to the source code directory and there running go build:

				
					go build
					ls -al
					total 1476
					drwxr-xr-x 2 gopher users    4096 Dec 25 11:31 .
					drwxr-xr-x 3 gopher users    4096 Dec 25 12:08 ..
					-rwxr-xr-x 1 gopher users 1496747 Dec 25 11:31 hello
					-rw-r--r-- 1 gopher users      88 Dec 25 12:09 hello.go
				
			

As you can see, the working directory not contains the executable file hello. Cross-compilation with Go is just this easy!

Step 4: Run on the pure.box

There are various ways to transfer the binary to the box: In addition to access via FTP, the box can be directly incorporated into your Windows network via SMB.

Since the simplest way to try out an application is to manually run it in a terminal session, SSH should be enabled on the box. This makes data transmission via SCP obvious.

If you have no yet installed an SSH client, install the package open-ssh. For SCP you will need the following parameters: The user name is "admin", the password is the administratorpassword you set. As host name specify host name or the IP address of your pure.box.

Copy file:

				scp hello admin@hostname:/data/userfiles
			

Run program:

Connect to the pure.box with Putty or using the ssh-command.

					
						ssh admin@hostname						
					
				

Then run the file hello in the directory /data/userfiles.

					
						./hello
						Hello pure.box
					
				

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